As consumer use of the Internet for medical information grows, continuing evaluation of the medical content on the Internet is needed. We evaluated Internet sites describing breast magnetic resonance imaging (MRI), an emerging technology tool in breast cancer diagnosis and screening. We searched Google for sites describing breast MRI and abstracted the affiliation, content, media type, readability, and quality of 90 most popular unique sites. Over half (56%) of the sites were commercially sponsored. The content varied by site and included medical and procedural facts, information about clinical trials, grants and journal articles, as well as human interest stories. Most (82%) sites described potentially beneficial uses of breast MRI, such as further evaluation of newly diagnosed breast cancers (58%); screening women at high risk for breast cancer (54%); evaluation of abnormal breast findings (48%); screening women with dense breasts (48%) or implants (27%); and surveillance for breast cancer recurrences (24%). Approximately half (56%) of the sites described the limitations of breast MRI, most commonly false positive findings (44%) and costs (24%). Website quality, including the display of contact information, sponsorship, currency of information, authorship, and references varied. The reading level was close to high school graduate. Internet sites describing breast MRI were mostly commercially sponsored, more often described the potential beneficial uses of the procedure than its limitations, and were of variable quality and high reading level. With the lack of enforceable standards for display of medical information on the Internet, providers should encourage patients to direct their searches to the most credible sites.